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Title: RESIDUAL TRIOSE PHOSPHATE ISOMERASE ACTIVITY AND COLOR MEASUREMENTS TO DETERMINE ADEQUATE COOKING OF GROUND BEEF PATTIES

Author
item SAIR, ARNOLD - MICHIGAN STATE UNIV
item BOOREN, ALDEN - MICHIGAN STATE UNIV
item Berry, Bradford
item SMITH, DENISE - MICHIGAN STATE UNIV

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Foodborne illnesses associated with the bacteria E. coli O157:H7 and inadequately cooked ground beef patties have highlighted the need for a reliable indicator of thorough cooking. Because some hamburgers turn brown prematurely before reaching 160 deg F, regulatory agencies are reviewing and revising information given to consumers on cooking hamburgers. Regulatory agencies are concerned that many consumers are unwilling to use meat thermometers to insure food safety when cooking hamburgers. It has been determined that certain muscle enzymes undergo inactivation at internal patty temperatures required for destruction of harmful bacteria. This study evaluated the activity of triose phosphate isomerase (TPI) in beef patties cooked to 140, 150, 160, 170 and 180 deg F. TPI activity decreased by over 2/3 between 150 and 160 with no further decreases observed in patties cooked to either 170 or 180 deg F. While pink, uncooked dpatty color decreased with increased internal temperature, the results sho that TPI activity is as sensitive to changes in temperature as cooked patty color. After repeated freezing and thawing of hamburgers, activity of TPI was not as accurate as in fresh product in relating to cooked product temperature. TPI activity may prove to be a sensitive alternative to cooked color and temperature for consumers, once a useful test for in-home use is developed.

Technical Abstract: The objectives of this study were to 1) compare the use of triose phosphate isomerase (TPI) activity and internal color scores for determination of cooking adequacy of beef patties, and 2) determine the effect of frozen storage and fat content on residual TPI activity in ground beef. Ground beef patties (24.4 percent fat) were cooked to five temperatures ranging from 60.0 to 82.2 deg C. TPI activity decreased as beef patty cooking temperature was increased from 60.0 to 71.1 deg C, however, no difference (P>0.05) in activity (6.3 U/kg meat) was observed in patties cooked to 71.1 deg C and above. Degree of doneness color scores, a* values and b* values of ground beef patties decreased as internal temperature was increased from 60.0 to 71.1 deg C, however, temperature had no effect on L* values. TPI activity in raw ground beef after five freeze-thaw cycles did not differ from the control. Three freeze-thaw cycles of raw ground beef resulted in a a57.2 percent decrease in TPI activity after cooking. TPI activity of cooke beef increased during 2 months of frozen storage, but TPI activity in ground beef stored for 3 months or longer did not differ from the unfrozen control. While past research has shown color to be a poor indicator of adequate thermal processing, our results suggest that undercooked ground beef patties could be distinguished from those that had been adequately cooked using residual TPI activity as a marker.